Additive manufacturing (sometimes termed 3D printing) is used to fabricate complex three-dimensional structures out of a variety of materials, such as polymers, metals, and ceramics, at levels of resolution down to tens of microns. Load-bearing mechanical structures from gears to functional fuel nozzles for jet engines have been produced by these techniques.
The printing of polymers has been accomplished mainly by extrusion-based direct-write methods for thermoplastics and stereolithography (SLA) based photo-polymerization for both thermoplastics and thermosets. Printed polymers are lightweight but relatively weak. Thus, 3D printing is now moving toward manufacturing fiber-reinforced polymer composites. Industrial automated fiber placement (AFP) printers have been developed that can print continuous strand carbon fiber, Kevlar, and fiberglass reinforced polymer. These robotic placement printers are limited to reinforcement fibers with length scales greater than millimeters and geometries larger than centimeters with orientation control limited to the X-Y plane.